After applying the ideas, and reloading the datamodules in Delphi, some of you got datamodules that looked like forms in the designer. I’ve not seen this behaviour in the IDE myself, but it must be a bug somewhere.

I should have been clearer when writing about the solution for frames looking like forms in the designer from my post Delphi – Frames as visual Components – changing your inheritance: that solution also applies to datamodules. I hinted on that by writing This is caused by the fact that the IDE […] does not recognize as a designable class like TFrame or TDataModule, but only covered the TFrame case.

So time to cover the or TDataModule case as well. :-)
If your datamodule suddenly looks like the image on the right, and/or you get complaints about properties like ClientHeight, ClientWidth, OldCreateOrder, PixelsPerInch or TextHeight, then need to change your dfm file.

A dfm file for a datamodule that indirectly descends from TDataModule should not have the object keyword as the first like this listing:

If you change from object to inherited in Text-Mode manually you also need to switch to Designer-Mode to get and ignore all the Error-Messages.
If you don’t switch back, you get these messages on Runtime.